Getting Started with GIS Analysis Module 6

1. Getting Started with GIS Analysis Module 6 ESRI Virtual Campus Learning ArcGIS Desktop Training Course ESRI ArcGIS

2. Introduction • A GIS analysis involves visualizing and combining geographic data to derive new information. • A GIS analysis may be as simple as looking at a map and discovering patterns in the data • such as clusters of asthma cases close to a heavily trafficked freeway. • Some GIS analyses are very complex and involve many data layers and operations • such as an analysis to predict the spread of a contamination plume and its possible effects on a watershed • Can include many different operations and methods. • All analyses follow a process that includes specific steps

3. Learning Objectives • List the steps in a GIS analysis. • Interpret an analysis plan that includes GIS tools, criteria, and workflow. • Extend a layer attribute table by joining another table to it. • Create and modify a selected set of features using a series of attribute and location queries. • Explain the difference between attribute and location queries. • Examine analysis results through maps, tables, and reports. • Generate a report that presents the results of an analysis.

4. Analytical Process • Usually includes seven steps • Define the problem • Define the criteria • Identify the data you need • Plan the analysis • Prepare the data for analysis • Execute the analysis • Examine and present the results

5. Analytical Process • May need to repeat at least some of the steps in order to refine or adjust analysis • While planning analysis (step 4), an additional feature class is needed, go back and identify another data source (step 3) • Examining analysis results (step 7) leads to criteria modification (step 2) and repeating of the analysis.

6. Getting Specific • First three steps are key • Clearly define the problem to be analyzed • Define the criteria that will direct the analysis • Identify the data you will use

7. Define the Problem • Not always an easy task • Try to describe scope of the analysis in one or two sentences • If broad • Break into several smaller parts that can be individually analyzed • "What sections of beach are most likely to suffer damage in a hurricane?" • Might need to be analyzed in three parts: • What sections of beach have had a high rate of erosion? • What sections of beach are not protected from urban development? • What sections of beach have both high erosion and are unprotected?

8. Define the Problem • GIS analysis doesn't actually solve a problem • Utilizes data and derives information from it • Analysis results • A person (or group of people) uses the information to make a decision • Hopefully solving the problem

9. Define the Criteria • Define what criteria is going to be used • In terms of specific distances, measurements, or attributes • In the previous example • Just how much erosion is a high rate? • Two feet per year? • Five feet per year? • The answer may depend on the purpose of your analysis, a scientific methodology you are following, or the data that is available.

10. Identify the Data • What feature classes and attributes are needed to find features or locations that meet the criteria? • Beach erosion problem • Beach sampling stations with attributes containing beach erosion rates or measurements • Urban areas or land use zones. • List data that might be needed for orientation or for presentation of the analysis results • i.e. a coastline layer • Investigate metadata • Data source, purpose, permissions, coordinate system, and attribute descriptions

11. Planning the Analysis • Creating an analysis plan • Can prevent mistakes and save time when executing analysis • Additional data may be needed • Test a particular approach or tool • Diagram a plan or tool to identify • Sequence of steps • Specific tool to use at each step • Data required and produced by each tool

12. Planning the Analysis • Workflow for finding parcels that would be affected by a street widening project • Identifies data layers and GIS tools to be used and shows proper order for entire process

13. Preparing the Data • Identify steps needed to prepare data • Add a field to a table • Edit or update features • Correct data errors • Change or define coordinate systems

14. Execute the Analysis • If planning process was thorough • executing the analysis should be straightforward • Follow the workflow diagram steps • It's always a good idea to perform the analysis using a copy of the data • Especially important if analysis includes processes that change the original feature class, table, or database • i.e. combining feature classes, calculating new attribute values, or adding or removing features

15. Examine and Present the Results • Doesn't always accomplish the desired results the first time through • Iterative process • Verify results and visually analyze the data produced by intermediate steps as well as the final analysis • When verifying results, consider: • Are the results what you expected? • Does it appear that the process you performed worked correctly? • Evaluate results in relation to the original analysis goal • Do the results answer your geographic question? • Is this new information valid or useful?

16. Examine and Present the Results • Draw conclusions from analysis results • Produce an output to share with others • On a land use planning project • Create and print one or more maps that can be reviewed by the planning commission or the general public • Analysis of a lake's water quality • Create maps, graphs, and tabular reports • Analysis results may • suggest that a decision or action is needed • raise new questions

17. Examine and Present the Results • Results of a water quality analysis • Presented in a map and graph • Map shows water quality sampling station locations • Graph shows water quality trends

18. Exercise • Define a Problem and Choose Data for Analysis

19. Asking Questions and Getting Answers • GIS analysis may involve visualizing data to identify patterns and relationships • sometimes looking at a map isn't enough • find features that match given criteria • Do this by querying the GIS database • Asking questions • Answer is a selected set of features

20. Two Types of GIS Queries • Attribute • Select features that have one or more attribute values that meet a particular criterion • In a city layer with a population attribute • Select all the cities with population greater than 1 million • Location • Select features whose location meets particular conditions • Usually in relationship to other features • In a cities layer and a major highways layer • Select all the cities that are within 50 kilometers of a major highway

21. Asking Questions and Getting Answers • Work with features once they are selected • Zoom • A selected set is temporary • Can be saved as a separate layer or exported to a feature class

22. Finding Features by Attribute • To find features that meet specific attribute criteria • Create a query expression • A logical statement consisting of three parts: • a field name (attribute) • an operator • an attribute value • Can be linked together to include multiple criteria • Compound expressions

23. Query Expressions • Top example • Simple • Population greater than 50,000 • Bottom example • Compound • Two attributes are being queried • Capital cities whose population is greater than 50,000

24. Finding Features by Attribute • Result of the query • Selected set of the features in the layer • Features are selected on the map • Corresponding records selected in the layer attribute table

25. Finding Features by Attribute • Cities with a pop >200,000 • Selected on the map, • Records are selected in the layer attribute table • Resulting from the query expression POP2000 > 200000

26. Finding Features by Attribute • Definition query • Query expression is a property of the layer • defines which features from the feature class will be included in the layer • Eliminate features that aren't of interest from the map display • Saves processing time when the layer is queried or used in another GIS operation

27. Finding Features by Attribute • Cities layer • definition query limits layer features to cities with a pop >200,000 • Map is much less cluttered

28. How do I know the proper format for building an expression? • ArcMap uses a standard computer language called Structured Query Language (SQL) for query expressions. • SQL is also used by ArcMap to access and manage databases • Most of the time you won't need to worry about the details of SQL because you will build your expressions by choosing options in a dialog

29. Finding Features by Expression • To find features whose location meets a criteria • Use a query expression • A location query is a descriptive statement • Has three parts: • a target ("select from") layer • a type of spatial relationship • a spatially related layer

30. Finding Features by Expression • Location query statement specifies • Layer to select features from • A type of spatial relationship • Layer you are comparing the first layer to

31. Finding Features by Expression • Can create location queries based on • Spatial relationships between features in the same layer or in a different layer • Can choose from many different spatial relationships • Four main categories of feature spatial relationships • Distance • Containment • Intersection • Adjacency

32. Finding Features by Expression • Buildings that are contained by historic preservation features (orange polygons) are selected.

33. Working with Selected Sets • Examples of what you can do with a selected set of features. • Visually analyze the geographic distribution of the selected features in the map • Summarize or calculate attribute values only for the selected features • Create a buffer around the selected features • Edit the selected features • Generate a report containing attributes of the selected features • Save the selected features as a new map layer that you can display and symbolize independently • Export the selected features to a new feature class to use in other map documents, share with others, or use as input for other GIS operations

34. Working with Selected Sets • Use a series of queries • To find features that meet a number of criteria • Additive approach • Features are added to the selected set with each query • Subtractive approach • Features are removed from the selected set with each query • Which approach depends on criteria • Approach that reduces processing time

35. Working with Selected Sets • Can select features by attribute before selecting by location • Interstate 70 selected using an attribute query • A location query found cities within 50 miles of the selected highway

36. Accessing More Attributes • Not all feature attributes are stored in a layer attribute table • User-defined attributes • Stored in separate, nonspatial tables • Associate a nonspatial table to the layer attribute table • If they share a common field • A field that stores the same data

37. Accessing More Attributes • The layer attribute table and the economic statistics table both contain a text field that stores two-letter abbreviations for each Canadian province. • The tables can be associated because they have this field in common.

38. Associating Nonspatial Tables • Two methods • Joins • Relates • Table joins • One-to-one • Each feature has one related record in the other attribute table. • Canadian provinces tables - each province has one unemployment record • Many-to-one relationships • Multiple features may have the same related record • A layer attribute table containing records for several job training offices within each province, related to the same economic statistics table

39. Associating Nonspatial Tables • When tables are joined • Fields from one table are appended to the other table. • Table joins are virtual • Tables appear connected in ArcMap • But fields from the nonspatial table have not actually been added to the layer attribute table. • Table joins are not permanent • Can remove a table join

40. What about table relates? • Table relates are designed for • One-to-many • Many-to-many relationships • Based on a common field • It doesn't append the attributes of one table to the other • Can access the related data when necessary

41. Exercise • Perform a GIS analysis

42. Examining and Presenting the Results • Graphical and tabular displays can be combined • Include a table in a map layout • Insert a map or graph into a report • How do you decide what to present? • If analysis project produced a lot of new info • Present only the highlights • Spatial information • Best presented in a map • A list of features and their attributes • Better presented in a table or report. • Easily compare attributes to show trends • A graph

43. Presenting Data in Maps • Maps created while conducting an analysis • Probably not suitable for presenting final analysis results • Prepared quickly • Needs to be visually simple

44. Presenting Data in Maps • Map used for executing an analysis • Has basic symbology • Only essential layers

45. Presenting Data in Maps • A presentation map should include info that explains its context and purpose • Add data layers for orientation • such as streets, landmarks, or administrative boundaries • Carefully choose map symbology to • Conform to common convention/industry standards • convey intended message • Label more features • Add callout text or graphics • To draw attention to important features, relationships, or analysis results

46. Presenting Data in Maps • Map includes • Features and labels to provide geographic context • Detailed symbology • Map focuses on analysis results • Limits sedge species shown to two: those found exclusively within 100 meters of the shoreline

47. Presenting Data in Reports • Organize, format, and print tabular • Examples of how you can customize a report: • Choose which attribute fields to include • Include all records in a table or a selected set • Sort records based on values in one or more fields • Group records and calculate summary statistics • Sum, average, and count • Choose elements to include • Title, image, or page number • Choose • Tabular format  Fields across the page • Columnar format  fields down the page

48. Presenting Data in Reports • ArcMap's built-in report generator • Create simple reports to add to a map layout • Alternative to adding a table

49. Presenting Data in Reports • Report created with ArcMap's report tool

50. Presenting Data in Reports • To create a report that to use more than once • Save it to a file on disk • Can export reports to different file types • Adobe Portable Document Format (.pdf) • Rich Text Format (.rtf) • Plain text (.txt)